Apparatus for fabricating mercury switches and the like



March-19,' 194s. C. H'. LAR-SON 2 'Sheets-Sheet APPARATUS FORF-ABRIGATING-MERCURY SWITCHES AND THE LIKE Filed .Junev 25, 1945/////////7/////////fy j `Marsh 19,. 1946. c, H, LARsoN APPARATUS FORFABRICATING MERCURY SWITCHES AND THE vLIKE Filed June 25. 1943 2sheets-sheet 2 I,

Ill/lll I viv? Mw www www w vWJ Patented Mar. 19, 1946 4carl n. Larson,Elkhart, 1mi., assigner to 'The Adlake Company, 'a corporation ofvIllinois Application June 25, 1943, Serial No. 492,329

12 Claims.

v1n fabricating mercuryswitches using'steel envelopes, it is importantto have the .envelopes hermetically sealed to withstand an 'internal gas-fpressure ora hundred pounds Yor more. it is preferable to useweldingimethods to vsealithe envelope but ythe .fact that one of theelectrodestwhich enters the envelop must ,be insulatedirom the base byglass .or equivalent insulating material introduces `a .complicationVbecause the heat of Welding will, unless proper .precautions :aretaken, destroy the Aseal between the electrode and the switch envelope.y

.-Heretofore, mechanical meanshad been yused for crimping the margin ofthe switch envelope against the .base but :this method of sealing vvthe`envelope is not .capable of withholding the high pressures which it isdesirable to carry within 'the .switch envelope. l

lThe ,present invention, although directed primarily to apparatus forfabricating mercury switches using steel envelopes, is also applicableto other :articles wherein it `is ldesirable 'to heat join a base to atubular envelope :of vsome kind. It is particularly applicable where aportion of the base has 'an electrode or similar-:conductor sealedthrough the base with a heat `sensitive sealing medium.

I-t is, therefore, v one of the principal objects of the invention toprovide apparatus for :use in heat joining a base to a tubular envelope.and mor-e particularly provide such method and .apparatus for use inthe `manufacture of metal envelope electrical devices which arenecessarily hermetically sealed.

`Other objects include the following: To provide apparatus which willaccommodate switches lor similar devices of different sizes for themaking `of .a hermetic seal; to localize the lapplication of heat duringthe operation of joining ithe :base to the switch envelope and therebyprotect adjacent parts of the switch from damage due to heat; to providean .apparatus which will operate satisfactorily for welding both ends ofthe switch structure onto the switch envelope; and to provide suitableadjusting devices to suit the application to the particular use forwhich the apparatus is being employed.

Further objects and advantages become .apparent as the disclosureproceeds land the description is read in conjunction with theaccom-panying drawings in which:

Fig. 1 is a vertical cross sectional view through apreferred form of theapparatus.; p

Fig. 2 is a sectional View showing the switch Atop closure cap in placeprior to welding;

Fig. :v3 'la lhorizontal .sectional 'view taken-.on .the-line :3 3 IofFig. 1i;

4 shows ya slightly different .method of sealing the `electrode into theswitch base; and

VFigli :is a vertical sectional Vview through :the

illustrative orm `:of 'a :metal `envelope mercury switch.

Butthe vspecific L'illustrations shown in the drawings :and hereinafterdescribed .merely..rep resentdesirablevforms in which the .invention mayybe..ernbodiedand appended claims should be construed `as :broadly fasAthe :prior .art will permit. In :the preferred `fcrm .of the invention,the apparatus .is :mounted on :a platform il l] :and conisists of a.base casting il having a vertical bore l2 andasiderbore 13. Thev twobores merge at thetop to ferm qan enlarged :chamber H .adapted to`receive the rotatable vhollow hub .I5 having `:downwardly facing gearteeth It adapted -tomesh with a .pini-on l1 driven-in a 'suitable mannerat a relatzlviely `slow and controllable speed .through the vshaft 1:8whichis :journalled in an yarm |i9 of the .hase casting I1.

The hub I5 is laterally extended at 20 to lprovide a V,seat fort-he tank2l which is circular in form `and .rests uponjand is secured to the seat,21.0. The tank .is yadapted to contain a cooling .fluid22 such aswater, the level of kwhich is maintained by an outlet tube 23 to whichsuctionis applied to .draw 01T any water above the bottom edge 2d of thetube. Waterzis admitted tothe tank through an inlet pipe '25 whichprojects downwardly into the cooiing fluid a substantial distance .andwhich serves as a stirrer to maintain circulation-fof the Water when thehub l5 .and tank 2 I are rotated.

Preferably, the base 1i, hub l5 and tank 2l,

vas Well `as allother parts of the apparatus which Ecorne in contactwith Athe Water, are made `of brass to avoid corrosion.

Thelhub .i5 has a vertical .bearing y2li whichflts into the .machined.bearing surface 2l provided .at the 'upper .portion of the ibase Il andthe weight :of the hub Aand the tank structure is carried -on ahorizontal bearing 28.

rihe bore 2f9 of the hub l5 is enlarged above the bearingas'shown at 3i)to provide -a seat 3| adapted to receive A.and support the tubularmember which is to .-behe'a-t joined to a base.- The shoulder ,or yledge3l may be raised to accommodate shorter switches by inserting spacersleeves which rest upon the led-ge Si and provide an upper surface torece-ive the shorter switch envelope. When switch envelopes of smalleroutside diameters are lto be used in the apparatus,

can be interchangeably mounted on the base Il to accommodate theswitches of diierent sizes.

Before describing the method in whichthe ap-l paratus is used to heatjoin a base t`o ai tubular member, it will be helpful to understand theprecise construction of an illustrative form of mer' cury switch whichmay be advantageously fabricated in the apparatus. l

Referring, therefore, to Fig. 5, it will be seen that the switchcomprises a tubular envelope 32 of non-magnetic material, preferably of18-8 stainless steel, and having both .ends ofv the envelope beveled offas indicated at 33. A base 34, preferably made of a materialvknown asKovar manufactured by the Stupakoff Ceramic and` Manufacturing Company,Latrobe, Pennsylvania, is formed, by stamping, into a cup-shaped cap asv shown and it has a central opening 35 through which an electrode 35 issealed by a heat sensitive material, preferably either 733A or 704 glassmade by vthe Corning Glass Works of Corning, New

York. This material is found most advantageous because it has acoeicient of expansion substantially the same as the Kovar material ofwhich the base 34 is preferably formed and substantially the same alsoas that of molybdenum which is the material preferably used for theelectrode 36. However, other combinations of material may be used forthe sealing of an `electrode through a base but in any case, the sealingmaterial is likely to be heat sensitive and must be protected when thebase 34 is heat joined, as for example by torch welding, to the reducedend 33 of theswitch envelope.

A glass sleeve 38 is telescoped over and fused to the electrode 35, andsince the electrode ma- Vterial and glass are chosen with likecoefficients of expansion, the glass will adhere to the electrodewithout cracking even under severe temperature changes. The glass sleeve38 is enlarged near the lower end 39 of the electrode to form a bead 3'!which, with the proper application of heat, may be iirmly fused to theseat 40 of the base 34, with'a portion of the glass overlaying andinterlocked with the top margin4l thereof, thus forming a strong andsecure insulated bond for the electrode and the base 34.

Lead wires 42 and 43 aresoldered to the electrode 36 and base 34,respectively, so that the mercury to now over the top of thev cup 48,the

electrical circuit is closed, and when that condition does not exist,the circuit is open.

A time delay thimble, generally designated 43, is telescopedovertheupper portion of the electrode 35 to delay the movement ofmercury to switch envelope are counterbored, as shown at 58,l

and/or away from the mercury 41. in the cup 48 in proportion to the timerequired for gas rto pass through the ceramic plug 5i] mounted inthe topof the thimble 49 to equalize the gas pressure differential caused byshifting of the mercury level by the displacer. Since the presentinvention is not concerned with the particular details of the time delaymeans, it will be Suilicient to refer to Larson Patent No. 2,232,874 fora fuller disclosure of this structure.

The plunger or displacer 45 is preferably made of high grade magneticiron and it is provided at both ends with a reduced portion 5l adaptedVtoV receive a non-magnetic steel spring 52 which is frictionally heldon the reduced portion 5l of the displacer. The springs 52 may be madeof the same material as the switch envelope 32; namely, 18-8 stainlesssteel in the austenitic form and the use of this material prevents thedisplacer 46 from adhering to the top closure 53 when it is made of coldrolled steel or other magnetic material.

In making up a metal switch of the type shown in Fig. 5, the electrode36 is rst fused to the insulating sleeve 38 and then the mercury cup 48and time delay thimble are applied to the upper .end of the electrode.The cap 34 is then slipped over the lower end of the insulated electrodeand a bead is formed adjacent to the lower end 39. The electrodeassembly is then inverted and the base 34 is drawn upwardly toward theend 33 of the electrode to be fused with and bonded to the bead formedat that end of the electrode. The complete sub-assembly consisting ofthe base 34 and the electrode bonded therethrough Awith the time delaystructure mounted on -the upper end of the electrode is then ready forbeing heat joined to the tubular envelope 32. Referring again to Fig, l,the tank 2i is iirst filled with water and it will overflow through thehub l5 into the drain outlet i3 in the base l l. Upon inserting a switchenvelope blank 32 into the bore 3U of the hub, the water level will risefrom the top of the hub i5 to the level determined by the position ofthe bottom edge 24 of the outlet tube 23, this level being designed tobe slightly below the beveled end 33 of the envelope 32 and placing theexposed portion of the switch envelope immediately below the b'evel incontact with the water in the tank. A tube 54 connected through aflexible hose 55 to a source of water supply, the volume of which iscontrolled by a valve 55, is then inserted through the bore I2 of thebase Il until its upper edge 51 is in the approximate position shown inFig. l and then a small volume of water is permitted to flow through thetube 54 to provide a fountain effect at the top which will adequatelybathe the lower portion `of the electrode seal when the base assembly isslipped into place.

' 'It will be seen in Fig. 5 that the ends of the to provide a seatwhich receives the base 34 and supports it in position. The outsidediameter of the portion 53 of the base is made such that it has a lightdrive t with the reduced ends of the envelope 32 so that when the baseassembly is slipped into place for being welded to the envelope, it willsecurely hold its position. It will hub t bya -Phosphor bronze spring 6iand with the l'base assembly in place, as shown in Fig l, a weldingtorch, -shown v-in ldotted lines -at 62 and whichmay -beconveniently`supported upon a rest :53, is applied to the upstanding mating edges ofthe 'envelope `and the base while the tank, the

hub, .the switch -envelope and :the base are rotated slowly through theshaft I8. By holding the torch steady and by rotating the work `aneven.weldcan be vconsistently obtained while the heat Vof the weld is .beingheid locally to the Ipoint Vof application. The water in the tank '2|effectively cools `the exterior .of the switch envelope while the waterbeing passed upwardly `throvugh ,the tube 54 isdirected against theglassseal andkeeps .it sufflcientlylcool so that heat travelling through the-base from the weld will not fracture or disrupt the .electrode seal. It.has been found suiiicient in protecting the kexternal portion oftheseal .to provide a metal .or .ceramic wide mouthed shield whichtelescopes over the projecting `end 3S of the electrode 35 and protectsit from the .direct flame of the torch.

The provision ci means for supplying a copious quantity kof coolingfiuid to the underside of the base during the welding or other heatjoining operation is of `considerable importance because :there Ais noconvenient way to inspect the bond within the envelope after the vbaseis afXed to the switch envelope. v

A skilled operator will soon know how much water to have flow throughthe tube 5d and where to ladjust `the top 5i of the tube 54 in order toprotect the seal during the heat joining operation.

Preferably, the tube 151i passes through a gland Gli where it may beheld in any desired vertical position by a set screw 55 locked in placeby lock vnut 65.

'After the base assembly has been welded into place, the switch isremoved from the lhub land the excess water flows out through the top ofthe hub l5. The switch is then returned to its nor- Amal uprightposition, iilled with mercury, pretested for operating characteristicsand then placed bac-k in the apparatus of this invention to have the top53 weldedinto place. The method `of welding the top 53 to the switchenvelope is identical with that already described except that the tubeE13 is removed as it must be to accommodate the switch base and thecooling of the switch during the welding operation is done entirely fromthe outside -by the water 22 in the tank 2 i. Since there is no bond ofheat sensitive material 4in the top, the outside cooling is Vadequate.

` A modified form of seal for the electrode is shown in Fig. 4 and itconsists of `a base 6l having a neck S3 terminating in an outwardlyflared throat E9 so that when a bead is formed on the glass sleeve 33slightly above the point of application of the base and the base isslipped upwardly with the simultaneous application of heat to form theseal shown in Fig. 4, the actual juncture between the glass and the baseEl is substantially removed from the place where the base `is welded tothe envelope as shown at lil. Hence, the cooling of this bond during thewelding operation by the water being passed upwardly through the tube 54is more readily and more fully accomplished.

The spacing of the tube 54 from the interior wall of the switch envelope32 (Fig. l) may be accomplished in Various ways, all that is requiredbeing that some form of spacer be employed to centrally locate the tube54 within the hub so that the central electrode structure cannot bedamaged by movement of lthe tube within the hub. Inl the :form of theinvention shown, the 'upper portion of -the pipe 2id iis `'formed ofhexagonal Abar stock `and is turned Idown to 'leave spacers --'i -asshown :in Figs. V1 and '3. This section of the -tube is then:brazed-tc'fthe 1lowerportion -of .the tube as shown at i2. f

' There -is sufficient roomrbetween the time delay .thimble 49 and the-inner walls of the tube 5d .to accommodate -theurela'tiveiy -smallvolumel of iiowwhich passes through the tube 5t.

After Aa switch -lhas -been completely fabricated, with .the .exceptionof inserting the gas fill, :it is placed in another machine where thegas fill is introduced through .a'looseiitting steel .pin i3 (Fig. 151)'which is. welded into .place when -the proper -gas dill haslbeenintroduced ythereby-completing a ihermeticsealing .of .the entireswitch-envelope.

I claim:

Y1. In apparatus foraflixing a metal base to a tubular steelenvelope,the 4combination of a iiuid tank containing .a ,cooling fluid, a hollowrotatable 'hub .projecting upwardly .into the tank,

means .for .supporting the envelope within the hub with `the top portionof the envelope `projectingslightlyfabove the fluid level in the tankand Vwith the .portion immediately below in contact with said fluid,said `projecting end of the envelope having a ledge adapted to receiveand support the vbase whereby the base may be heat joined to theenvelope, means for rotating the hub and envelope ,duri-ng the heatjoining operation, and means'for direct-ing a stream of cooling Afl-uidupwardly -through the yhub against'the bottom side of the base duringthe heat joining operation.

2. In apparatus for ani-Xing -a base te a tubular switch envelope by theapplication of heat, said base being of the type having an electrodeextending through the ibase and bonded therein with a heat sensitiveAsealing medium, the combination of a Vtank containing a cooling huid, ahollow hub projecting upwardly into the tank, means forsupporting theenvelope in the hub with the upper portion slightly projecting above thefluid level and withthe portion immediately below in contact 'with thefluid, said projecting end of the envelope having a ledge adapted toreceive and support the base whereby the base may be Vheat joined to theenvelope, and means for direc-ti-ng a stream of cooling fluid upwardlythrough the hub and envelope against the sealing medium at the electrodebond in the base.

3. In apparatus for afxing a base to a tubular switch envelope Vby theapplication of heat, said base being of the type having an electrode eX-tending through the base and bonded therein with a heat sensitivesealing medium, the combination therewith of a hollow hub, means forsupporting the envelope in the hub, said envelope having a surfaceadapted to receive and support the base, and means including a tubeloosely telescoped within the hub and envelope for directing a stream ofcooling fluid against the sealing medium on the inner face of the basewhen the base is being heat joined to the envelope and for causing it tobe expelled through the space 'between the tube and the envelope.

4. In apparatus for aiiiXing a base to a tubular switch envelope by theapplication of heat, said base being of the type having Aan electrodeextending through the base and bonded therein with a heat sensitivesealing medium, the combination therewith of a hollow hub, means forsupporting the envelope in the hub, said enelectrode to protect theelectrode bond while heat Y is being applied to unite the base with theenvelope.

5. In apparatus for aillxing a base to a tubular switch envelope by theapplication of heat, said base being of the type having an electrodeextending through the base and bonded therein with a heat sensitivesealing medium, the combination therewith of a hollow hub, means forsupporting the envelope in the hub, said envelope having asurfaceadapted to receive and support the base, and means including atube loosely telescoped within the hub and envelopefor directing astream of cooling iiuid against the sealing medium on the inner face ofthe base 'when the base is being heat joined to the envelope and forcausing it to be expelled through the space between the tube and theenvelope, and means for rotating the hub, the envelope and the baseduring the application of heat.

6. In apparatus for alxing a, metal base to a tubular steel envelope,the combination of aV iluid tank containing a cooling fluid, means forcirculating fluid through the tank and for maintaining a constant leveltherein, a hollow hub projecting upwardly into the tank, means forsupporting the envelope within the hub with the top portion of theenvelope projecting slightly above the fluid level in the tank and withthe portion immediately below in Contact with said iiuid, saidprojecting end of the envelope having a surface adapted to receive andsupport the base whereby the base may be heat joined to the envelope,and means for. rotating the tank, the hub, the switch envelope and thebase during the application of heat for joining the base to theenvelope.

7. In apparatus for aixing a metal base to a tubular steel envelope, thecombination of a fluid tank containing a cooling fluid, a hollow hubprojecting upwardly into the tank, means for supporting the envelopewithin the hub with the top portion of the envelope projecting slightlyabove the iiuid level in the tank and with the portion immediately belowin contact with said iiuid, said projecting end oi the envelope having asurface adapted to receive and support the base whereby the base may beheat joined to the envelope, and means for directing a stream of coolingfluid upwardly through the hub against the bottom side of the baseduring'the heat joining operation.

8. In apparatus for aixing a base to a tubular supporting the envelopein the hub, said envelope having a surface adapted to receive andsupport the base, and means including a tube telescoped over theinwardly projecting portion of the electrode and telescoped looselywithin the hubv and the envelope for directing a, stream of coolingluidagainst the sealing medium on the inner face of the base when thebase is being heat joined to the envelope and for causing it to beexpelled through the space between the tube and the envelope, said tubebeing removable from the hub.

9. In apparatus for aiiixing a base to a tubular switch envelope by theapplication of heat, said base being of the type having an electrodeextending through the base and bonded therein with a heat sensitivesealing medium, the combination therewith of a hollow hub, means forsupporting the envelope in the hub, said envelope having a surfaceadapted to receive and support the base, and means including a tubetelescoped over the inwardly projecting portion of the electrode andtelescoped loosely within the hub and the envelope for directing astream of cooling uid against the sealing medium on the inner face ofthe base when the base is being heat joined to the envelope and forcausing it to be expelled through the space between the tube and theenvelope, and means for adjusting the ilow of cooling fluid through thetube.

10. In an apparatus of the class described for use in heat bonding anend member to a tubular envelope, the combination of a tank having aninner hollow hub portion whereby the tank confines an annular body ofliquid surrounding said hub portion, means to support said envelope insaid hub with the envelope extending above the top of the hub andfitting closely enough in the hub to maintain the liquid in the tank ata higher level than the hub, and means for circulating cooling fluidwithin said hub to cool the upper end of said envelope from the insideand to cool the inner face of said end member when the end member ispositioned on the upper end of the envelope.

11. In an apparatus of the class described for use in heat bonding anend member to a tubular envelope, the combination of a tank having aninner hollow hub portion whereby the tank conf fines an annular body ofliquid surrounding said hub portion, means to support said envelope atsaid hub with the top portion of the envelope extending above the liquidlevel in the tank, a tube positioned in said hub portion to extend intosaid envelope to deiine within the envelope an inner fluid passage andan outer annular fluid passage, and means for forcing fluid into one ofsaid passages to return by the other of said passages for cooling theinside of the envelope.

12. In an apparatus of the class described for use in heat bonding anend member to a tubular envelope, the combination of a. tank containingcooling liquid, means to support said envelope in position with themajor portion of the envelope submerged in said liquid and a top portionof the envelope exposed for the heat bonding of said end member thereto,means to deliver a stream of the cooling liquid into said tank, means todrawV off cooling liquid from the tank at a point to vdetermine themaximum liquid level in the tank, means'to rotate the tank about an axisextending through the tank, and means extending into the tank to impedethe tendency of the liquid to rotate with the tank.

CARL LARSON.

